The present invention relates to a gas turbine engine, and more particularly to a bypass turbojet engine having a gas flow bleed system.
A bypass turbojet engine having a high bypass ratio comprises, in view of the direction of gas flow, a low pressure compressor followed downstream by a high pressure compressor which supplies compressed air to a combustion chamber. In the combustion chamber the air is mixed with a pressurized fuel and burned in order to apply power downstream the chamber to a high pressure turbine driving the high pressure compressor, and to a low pressure turbine positioned downstream and arranged to drive the fan and the low pressure compressor. The gases at the turbine exhaust apply a residual thrust in addition to the thrust generated by the gases moving through the bypass flow path.
Under certain flight conditions, for instance under reduced load in the course of aircraft descent, the airflow delivered by the low pressure compressor may be excessive for appropriate engine operation, and consequently a portion of the airflow must be deflected toward the bypass flow path to preclude a so-called xe2x80x9csurge phenomenonxe2x80x9d caused by the fluid filaments detaching off the blades which results in flow instability.
Moreover, when the aircraft passes through dense clouds, water in the form of rain or hail may enter the compressors. At full engine power, this water is vaporized and the steam is hot enough and sufficiently atomized so that the combustion chamber is not extinguished. During aircraft operations such as this, the combustion chamber receives a relatively high flow of fuel. On the other hand, when the aircraft is undergoing a descent or approach operation prior to landing, the engine turns slowly, and consequently the compression ratios of the compressor are comparatively low and water in the liquid or solid state is present therein. During this operation, the combustion chamber receives a relatively low flow of fuel. As a result, water may reach the combustion chamber and therefore extinguish some or all of the burners. The presence of large quantities of water in the combustion chamber, therefore, may lead to serious results.
Accordingly, turbojet-engine bleed device systems generally are used and include mobile scoops which, when driven by complex control means, enter the primary flow path in an annular space separating high and low pressure compressors. Because the angular space often has a gooseneck-shaped profile, and since water particles on account of their density are moving along the outer wall of the primary flow path, the particles may get trapped by the scoops and be deflected toward the bypass flow path.
British patent 2,259,328 discloses such a bleed system wherein the scoops are driven by a synchronizer configured in the intermediate casing so as to direct the diverted air and the particles toward stationary tubes that exhaust them into the secondary flow path downstream of engine support struts.
European patent 0,407,297 discloses the insertion of traps in the inner and outer walls of an inner flow path casing, whereby these traps are synchronized and radially displaced outwards.
European patent 0,374,004 discloses the use of traps that cooperate with a scooping device and are configured along the outer wall of the primary flow path.
In all of the aforementioned bleed systems, the devices driving the scoops and the traps are configured along the inner flow path and operate synchronously. These drive devices are arranged with a control ring, linkrods, hydraulic actuators or cables to drive traps or hinging scoops. These devices are fairly complex, and moreover difficult to access for maintenance and overhaul.
Accordingly, it is an objective of the present invention to create a bypass gas turbine engine wherein the bleed devices are generally constituted by stationary elements.
Thus, the present invention relates to a bypass gas turbine engine and in particular, to an aircraft bypass turbojet engine which, between the primary and the bypass flow paths, is fitted with a structural intermediate casing configured axially between a low pressure compressor and a high pressure compressor and further includes a bleed device implementing the deflection of a portion of the gas flow issuing from the low pressure compressor toward the bypass flow path.
This gas turbine engine is characterized in that the bleed device comprises an annular cavity operating as a manifold which is situated upstream from the intermediate casing along the outer wall of the primary air flow path and permanently communicates with the primary flow path. The bleed device further includes a plurality of substantially axial conduits disposed in the intermediate casing which are connected to the manifold, and a plurality of tubes configured around the high pressure compressor to permit communication between the conduits and the bypass flow path. Each of the tubes is filled with at least one regulating valve.
Advantageously, the intermediate casing and the conduits are cast as a single, integral unit. The intermediate casing includes a plurality of radial arms and the conduits are configured between the radial arms.
Preferably, the manifold communicates with the primary air flow path by means of a plurality of orifices defined along the outer wall of the inner flow path and of which form an inducer.
In a highly advantageous manner, the flow-regulating valves are driven separately one from another.
In this manner, when all of the regulating valves are in an open position, a high outflow of air is diverted from the primary air flow path and directed toward the bypass flow path by means of the annular manifold, the conduits and the tubes.
If only one regulating valve is open, only a slight airflow is fed from the primary air flow path. This low airflow is taken from the radially outer zone of the primary flow path which is rich in water particles. In this case, the bleed system acts as a particle trap. This function also applies when all the valves are set in a low output position.
The inducer separating the primary air flow path from the manifold leads to aerodynamic continuity of the primary flow path when the flow regulating valves are closed.
Integral with the intermediate casing, the conduits advantageously increase the mechanical rigidity of the intermediate casing.
The bleed device of the present invention is free of any moving parts in contact with the primary flow path and of any displaceable part in the structural intermediate casing. The flow regulating valves that are configured inside the tubes around the high pressure compressor and constitute assemblies which are easily exchanged for maintenance. Moreover, the invention is free of complex sealing means such as sealing elements around the traps and scoops.
Other advantages and features of the invention are elucidated in the illustrative description below and in relation to the attached drawings.